Stabilized power unit

ABSTRACT

A control section controls a switch to a charge period so as to charge a voltage-increasing capacitor at a start up. Then, the control section controls the switch to a voltage-increasing period so as to increase a voltage by a voltage-increasing capacitor and charges the output capacitor. The switching section alternately switches the charge period and the voltage-increasing period so that the charged voltage of the output capacitor, i.e., the output voltage is always stabilized within a range of the output voltage in a steady state. Here, a soft start circuit controls the switching section to carry out the switching operation so that the charged voltage always becomes not more than the output voltage in the steady state at the start-up.

FIELD OF THE INVENTION

[0001] The present invention relates to a switched-capacitor-typestabilized power unit.

BACKGROUND OF THE INVENTION

[0002]FIG. 19 shows a structure of a switched-capacitor-type stabilizedpower unit 101 for obtaining an output voltage twice as much as an inputvoltage. The stabilized power unit 101 is structured so as to include anintegrated portion 101 a, and a voltage-increasing capacitor C101, aninput capacitor C102, an output capacitor C103, and voltage-dividingresistors R101 and R102 provided outside the integrated portion 101 a.The integrated portion 101 a is provided with switches S101, S102, S103,S104, a control section 111, a comparator 112, and a reference voltagesource 113. Further, the integrated portion 101 a is provided with anoutput terminal T101 outputting an output voltage V_(o), an inputterminal T102 to which an input voltage V_(in) is inputted from a powersource such as a battery, a feedback terminal T103 for the outputvoltage V_(o), a GND terminal T104, a capacitor connection terminal T105to which an electrode C− having a lower potential of thevoltage-increasing capacitor C101 is connected, and a capacitorconnection terminal T106 to which an electrode C+ having a higherpotential of the voltage-increasing capacitor C101 is connected.

[0003] In the stabilized power unit 101, a switched capacitor section isstructured by the switches S101, S102, S103, S104, and thevoltage-increasing capacitor C101. The control section 111 controlsswitching operation of the switches S101, S102, S103, S104 in theswitched capacitor section. When the control section 111 controls theswitches S101 and S103 to be ON and the switches S102 and S104 to beOFF, and the input voltage V_(in) is applied to the input terminal T102via the input capacitor C102, the voltage-increasing capacitor C101 ischarged. Next, when the control section 111 controls the switches S101and S103 to be OFF and the switches S102 and S104 to be ON, therespective potentials of the electrodes of the voltage-increasingcapacitor C101 increase by the potential of the input terminal T102. Thevoltage increased by such an operation is outputted as the outputvoltage V_(o) via the output capacitor C103.

[0004] The output voltage V_(o) is detected by the voltage-dividingresistors R101 and R102, and a voltage V_(fb) 101 at a point connectingthe voltage-dividing resistors R101 and R102 is inputted to anon-reversal input terminal of the comparator 112. The comparator 112compares the voltage V_(fb) 101 with a reference voltage V_(ref) 101generated by the reference power source 113 and inputted to a reversalinput terminal. When the voltage V_(fb) 101 reaches the referencevoltage V_(ref) 101, the comparator 112 outputs a signal to the controlsection 111 so as to stop the switching operation of the switches S101,S102, S103, S104. The comparator 112 is a comparator having a hysteresisfunction, and when the switching operation is stopped and the outputvoltage V_(o) decreases, that is, the voltage V_(fb) 101 decreases, thecomparator 112 outputs a signal to the control section 111 so as toresume the switching operation of the switches S101, S102, S103, S104.By repeating the foregoing operation, the stabilized power unit 101stabilizes the output voltage V_(o).

[0005]FIG. 20 shows a time chart on the operation of stabilizing theoutput voltage V_(o) in the stabilized power unit 101. At time t₀, theswitches S101 and S103 are ON and the switches S102 and S104 are OFF,and the input voltage V_(in) is started to be applied, thevoltage-increasing capacitor C101 becomes charged, and the potential ofthe electrode C+ of the voltage-increasing capacitor C101 becomesV_(in). Next, at time t₁, the switches S101 and S103 are OFF and theswitches S102 and S104 are ON, and the potential of the electrode C+ ofthe voltage-increasing capacitor C101 becomes 2V_(in), a charge to theoutput capacitor C103 is started, and the output voltage V_(o) comes tobe increased. At time t₂, the respective switches are in the conditionsidentical to those at the time t₀, and the potential of the electrode C+of the voltage-increasing capacitor C101 becomes V_(in) again. At timet₃, the respective switches are in the conditions identical to those atthe time t₁, and the potential of the electrode C+ of thevoltage-increasing capacitor C101 becomes 2V_(in), and the outputcapacitor C103 becomes charged. In a period from the time t₂ to the timet₃, since an output current flows from the stabilized power unit 101 toa load, a discharge from the output capacitor C103 is carried out, andthe output voltage V_(o) is decreased.

[0006] The output voltage V_(o) is increased by repeating such a chargeand a discharge to and from the output capacitor C103 in a predeterminedduty. When the output voltage V_(o) reaches a predetermined thresholdlevel COM1, that is, when the voltage V_(fb) 101 at the point connectingthe voltage-dividing resistors R101 and R102 reaches the referencevoltage V_(ref) 101, the comparator 112 outputs a signal for stoppingthe switching operation to the control section 111. Suppose that thisoccurs at time t_(k), the switches S101 and S103 are ON and the switchesS102 and S104 are OFF at the time t_(k), and the condition ismaintained. After the time t_(k), the output voltage V_(o) continues tobe decreased until it declines to a predetermined threshold level COM2,where the comparator 112 outputs a signal for starting the switchingoperation to the control section 111. Suppose that this occurs at timet_(n), the switches S101 and S103 are OFF and the switches S102 and S104are ON at the time t_(n), and the switching operation is started. Insuch a manner, the stabilized power unit 101 shifts from start-up stateto steady state.

[0007] However, in the foregoing conventional stabilized power unit 101,when the output voltage V_(o) increases very steeply, there is apossibility that the output voltage V_(o) might overshoot and some loadconnected to the stabilized power unit 101 might fail to functionproperly.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to provide aswitched-capacitor-type stabilized power unit which can prevent anovershoot of an output voltage at start-up, in a structure having anoutput capacitor which outputs a charged voltage obtained through aplurality of charges by switching operation utilizing avoltage-increasing potential of a voltage-increasing capacitor at thestart-up, as the output voltage.

[0009] To achieve the foregoing object, a stabilized power unit of thepresent invention is a switched-capacitor-type stabilized power unitstructured so as to include:

[0010] an voltage-increasing capacitor which is charged based on aninput voltage and whose voltage is increased after being charged;

[0011] switching section for carrying out switching operation toalternately switch a charge period and a voltage-increasing period ofthe voltage-increasing capacitor; and

[0012] an output capacitor which outputs a charged voltage obtained bybeing charged utilizing a voltage-increasing potential of thevoltage-increasing capacitor in the voltage-increasing period, as anoutput voltage, and stabilizes the charged voltage within a range of theoutput voltage in steady state through a plurality of thevoltage-increasing periods after a start-up is started,

[0013] wherein the stabilized power unit includes soft start means forcontrolling the switching section to carry out the switching operationso that the charged voltage always becomes not more than the outputvoltage in the steady state, at the start-up from when the start-up isstarted until when the charged voltage is stabilized within the range ofthe output voltage in the steady state.

[0014] According to the foregoing invention, at the start-up, the softstart means controls the switching section to carry out the switchingoperation so that the charged voltage of the output capacitor alwaysbecomes not more than the output voltage in the steady state. With thisstructure, the charged voltage of the output capacitor becomesstabilized within the range of the output voltage in the steady state,without having an overshoot until the completion of the start-up.Consequently, it becomes possible to provide a switched-capacitor-typestabilized power unit which can prevent an overshoot of the outputvoltage at the start-up, in the structure having the output capacitorwhich outputs the charged voltage obtained through a plurality ofcharges by the switching operation utilizing a voltage-increasingpotential of the voltage-increasing capacitor, as an output voltage.

[0015] Additional objects, features, and strengths of the presentinvention will be made clear by the description below. Further, theadvantages of the present invention will be evident from the followingexplanation in reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram showing a structure of a stabilizedpower unit in accordance with an embodiment of the present invention.

[0017]FIG. 2 is a circuit block diagram showing a more specificstructure of the stabilized power unit shown in FIG. 1 in accordancewith Example 1.

[0018]FIG. 3 is a circuit block diagram showing a structure of a dutyadjustment circuit of the stabilized power unit shown in FIG. 2.

[0019]FIG. 4 is a time chart showing an operation of the stabilizedpower unit provided with the duty adjustment circuit shown in FIG. 3.

[0020]FIG. 5 is a circuit block diagram showing another structure of theduty adjustment circuit of the stabilized power unit shown in FIG. 2.

[0021]FIG. 6 is a time chart showing an operation of the stabilizedpower unit provided with the duty adjustment circuit shown in FIG. 5.

[0022]FIG. 7 is a circuit block diagram showing a more specificstructure of the stabilized power unit shown in FIG. 1 in accordancewith Example 2.

[0023]FIG. 8 is a circuit block diagram showing a structure of anoscillation frequency adjustment circuit of the stabilized power unitshown in FIG. 7.

[0024]FIG. 9 is a time chart showing an operation of the stabilizedpower unit provided with the oscillation frequency adjustment circuitshown in FIG. 8.

[0025]FIG. 10 is a circuit block diagram showing another structure ofthe oscillation frequency adjustment circuit of the stabilized powerunit shown in FIG. 7.

[0026]FIG. 11 is a circuit block diagram showing a more specificstructure of the stabilized power unit shown in FIG. 1 in accordancewith Example 3.

[0027]FIG. 12 is a circuit block diagram showing a structure of a gatevoltage adjustment circuit of the stabilized power unit shown in FIG.11.

[0028]FIG. 13 is a time chart showing an operation of the stabilizedpower unit provided with the gate voltage adjustment circuit shown inFIG. 12.

[0029]FIG. 14 is a circuit block diagram showing another structure ofthe gate voltage adjustment circuit of the stabilized power unit shownin FIG. 11.

[0030]FIG. 15 is a time chart showing an operation of the stabilizedpower unit provided with the gate voltage adjustment circuit shown inFIG. 14.

[0031]FIG. 16 is a circuit block diagram showing a more specificstructure of the stabilized power unit shown in FIG. 1 in accordancewith Example 4.

[0032]FIG. 17 is a circuit block diagram showing a structure of areference voltage adjustment circuit of the stabilized power unit shownin FIG. 16.

[0033]FIG. 18 is a time chart showing an operation of the stabilizedpower unit provided with the reference voltage adjustment circuit shownin FIG. 17.

[0034]FIG. 19 is a circuit block diagram showing a structure of aconventional stabilized power unit.

[0035]FIG. 20 is a time chart showing an operation of the stabilizedpower unit shown in FIG. 19.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Referring to FIGS. 1 through 18, the following description willexplain one embodiment of a stabilized power unit of the presentinvention.

[0037]FIG. 1 shows a structure of a stabilized power unit 1 inaccordance with the present embodiment. The stabilized power unit 1 is aswitched-capacitor-type stabilized power unit, and is structured so asto include an integrated portion 1 a, and a voltage-increasing capacitorC1, an input capacitor C2, an output capacitor C3, and voltage-dividingresistors R1 and R2 connected outside the integrated portion 1 a.

[0038] The integrated portion 1 a is provided with an output terminal T1outputting an output voltage V_(o) applied to a load, an input terminalT2 to which an input voltage V_(in) is inputted from a power source, afeedback terminal T3 to which a detected value of the output voltageV_(o) is inputted, a GND terminal T4, and a capacitor connectionterminals T5 and T6 to which the voltage-increasing capacitor C1 isconnected, all of which are lead pin terminals.

[0039] Outside the integrated portion 1 a, an electrode C− having alower potential of the voltage-increasing capacitor C1 is connected tothe capacitor connection terminal T5, and an electrode C+ having ahigher potential of the voltage-increasing capacitor C1 is connected tothe capacitor connection terminal T6. The input capacitor C2 isconnected between the input terminal T2 and a GND line. The outputcapacitor C3 is connected between the output terminal T1 and a GND line.The voltage-dividing resistors R1 and R2 are connected in series betweenthe output terminal T1 and a GND line, with the voltage-dividingresistor R1 provided on the side of the output terminal T1. Besides, aconnecting point between the voltage-dividing resistors R1 and R2 isconnected to the feedback terminal T3. The GND terminal T4 is connectedto a GND line outside the integrated portion 1 a.

[0040] The voltage-increasing capacitor C1 is a capacitor which ischarged in accordance with the input voltage V_(in), and whose voltageis increased after the charge. The input capacitor C2 is a capacitorwhich is charged by a power source provided outside the stabilized powerunit 1 and applies the input voltage V_(in) to the input terminal T2.The output capacitor C3 is a capacitor outputting the output voltageV_(o) obtained by a charge utilizing a voltage-increasing potential inthe voltage-increasing capacitor C1, specifically, the output voltageV_(o) obtained by the charge in accordance with a potential differencebetween the voltage-increasing potential at the electrode C+ and a GNDpotential in a structure in which the output capacitor C3 is connectedin parallel with a circuit including the voltage-increasing capacitor C1and the input capacitor C2 which are connected in series, via the outputterminal T1. However, while the output capacitor C3 is being charged,the input voltage V_(in) continues to be applied to the input capacitorC2. The voltage-dividing resistors R1 and R2 constitute avoltage-dividing circuit for the output voltage V_(o), and the dividedvoltage of the output voltage V_(o) at the connecting point between thevoltage-dividing resistors R1 and R2, that is, the detected value, isinputted to the feedback terminal T3 as a feedback voltage V_(fb) 1.

[0041] In the integrated portion 1 a, on a path between the outputterminal T1 and the input terminal T2, switches S1 and S2 for connectingor cutting off the path are provided in series, with the switch S2provided on the side of the output terminal T1. Besides, on a pathbetween the input terminal T2 and a GND line inside the integratedportion 1 a, switches S3 and S4 for connecting or cutting off the pathare provided in series, with the switch S4 provided on the side of theinput terminal T2. Further, a connecting point between the switch S1 andthe switch S2 is connected to the capacitor connection terminal T6, anda connecting point between the switch S3 and the switch S4 is connectedto the capacitor connection terminal T5, respectively. A switchedcapacitor section is constituted by the switches S1, S2, S3, S4 and thecapacitor C1.

[0042] In addition, a control section 2 is provided for controlling ONstate (connected state) and OFF state (cut-off state) of the switchesS1, S2, S3, S4. The control section 2 outputs a signal a which makes theswitches S1 and S3 ON or OFF simultaneously, and outputs a signal bwhich makes the switches S2 and S4 ON or OFF simultaneously. With thisarrangement, the switches S1, S2, S3, S4 carry out switching operationfor switching the ON state and the OFF state.

[0043] The switching operation alternately switches a charge period inwhich the switches S1 and S3 are ON and the switches S2 and S4 are OFF,and the voltage-increasing capacitor C1 is charged by the application ofthe input voltage V_(in), and a voltage-increasing period in which theswitches S1 and S3 are OFF and the switches S2 and S4 are ON, and avoltage is increased in the voltage-increasing capacitor C1 and a chargefrom the voltage-increasing capacitor C1 to the output capacitor C3 iscarried out. In the charge period, the voltage of the voltage-increasingcapacitor C1 is determined by the input voltage V_(in) and the length ofthe charge period. In the voltage-increasing period, the potential ofthe electrode C− of the voltage-increasing capacitor C1 increases from aGND potential to a potential of the input terminal T2, the potential ofthe electrode C+ increases by the potential increase at the electrodeC−, and thus the voltage is increased. In the voltage-increasing periodin steady state, the potential of the electrode C+ becomes 2V_(in).Consequently, the output capacitor C3 is charged in accordance with theapplication of the voltage 2V_(in). The output capacitor C3 outputs acharged voltage obtained by being charged by the voltage-increasingcapacitor C1, as the output voltage V_(o).

[0044] Further, a comparator 3 is provided so as to input a signal c fordetermining timing to start or stop the switching operation of theswitches S1, S2, S3, S4, to the control section 2. A non-reversal inputterminal of the comparator 3 is connected to the feedback terminal T3,and a reversal input terminal of the comparator 3 is connected to a DCvoltage source 4 provided so as to generate and input a referencevoltage V_(ref) 1. The comparator 3 has a hysteresis function, andcompares the feedback voltage V_(fb) 1 inputted from thevoltage-dividing resistors R1 and R2 to the non-reversal input terminalvia the feedback terminal T3, with the reference voltage V_(ref) 1inputted to the reversal input terminal. When the feedback voltageV_(fb) 1 reaches the reference voltage V_(ref) 1, the comparator 3outputs the signal c which gives an instruction to stop the switchingoperation of the switches S1, S2, S3, S4, to the control section 2. Whenthe feedback voltage V_(fb) 1 decreases by a predetermined value thanthe reference voltage V_(ref) 1, the comparator 3 outputs the signal cwhich gives an instruction to start the switching operation of theswitches S1, S2, S3, S4, to the control section 2. The foregoingpredetermined value may be constant during the operation of thestabilized power unit 1, or may vary at the respective points.

[0045] Before the start-up of the stabilized power unit 1, the switchesS1, S2, S3, S4 are all OFF under the control of the control section 2.When the start-up is started, the control section 2 controls so that theswitches S1 and S3 become ON and the switches S2 and S4 become OFF, andthe switching operation is started from the charge period. Then, by theswitching operation of the switches S1, S2, S3, S4 after the start ofthe start-up, the charged voltage of the output capacitor C3 comes to bestabilized within a range of the output voltage V_(o) in steady stateafter a plurality of the voltage-increasing periods, regardless ofwhether the switching operation is stopped by the comparator 3 or not.The switches S1, S2, S3, S4, the control section 2, the comparator 3,the DC voltage source 4, and the voltage-dividing resistors R1 and R2constitute a switching section 5 as shown in FIG. 1, and the switchingsection 5 serves as switching means for carrying out the switchingoperation alternately switching the charge period and thevoltage-increasing period of the voltage-increasing capacitor C1.

[0046] The integrated portion 1 a is further provided with a soft startcircuit 6. The soft start circuit 6 serves as soft start means forcontrolling the switching section 5 to carry out the switching operationso that, at the start-up from when the start-up is started until whenthe charged voltage of the output capacitor C3 is stabilized within therange of the output voltage V_(o) in steady state, the charged voltageof the output capacitor C3 always becomes not more than the outputvoltage V_(o).

[0047] Up to this point, the structure of the integrated portion 1 a hasbeen described.

[0048] Next, the following description will explain the operation of thestabilized power unit 1 of the foregoing structure. First, when theinput voltage V_(in) is inputted to the input terminal T2 via the inputcapacitor C2 and the start-up is started, the signal a outputted fromthe control section 2 makes the switches S1 and S3 ON, and the signal boutputted from the control section 2 makes the switches S2 and S4 OFF.With this arrangement, the charge period is started, and thevoltage-increasing capacitor C1 becomes charged. Next, the signal aoutputted from the control section 2 makes the switches S1 and S3 OFF,and the signal b outputted from the control section 2 makes the switchesS2 and S4 ON, which switches the charge period to the voltage-increasingperiod in which the voltage is increased in the voltage-increasingcapacitor C1, the output capacitor C3 becomes charged, and the outputvoltage V_(o) is applied to the load. Afterwards, by alternatelyswitching the charge period and the voltage-increasing period, thecharged voltage of the output capacitor C3, that is, the output voltageV_(o), becomes stabilized at the output voltage V_(o) in steady state.Here, under the control by the soft start circuit 6, the switchingsection 5 carries out the switching operation at the start-up so thatthe charged voltage of the output capacitor C3 always becomes not morethan the output voltage V_(o) in steady state, so as to realize softstart.

[0049] Besides, after the start-up is started, the output voltage V_(o)is detected by the voltage-dividing resistors R1 and R2, and thefeedback voltage V_(fb) 1 at the connecting point between thevoltage-dividing resistors R1 and R2 is inputted as the detected valueto the non-reversal input terminal of the comparator 3 via the feedbackterminal T3. The comparator 3 compares the feedback voltage V_(fb) 1with the reference voltage V_(ref) 1 of the DC voltage source 4. Whenthe start-up is started, the feedback voltage V_(fb) 1 is lower than thereference voltage V_(ref) 1 by a predetermined value, and the comparator3 outputs the signal c which gives an instruction to start the switchingoperation to the control section 2, and thus the switching section 5carries out the switching operation. As the output voltage V_(o)increases, the feedback voltage V_(fb) 1 increases and reaches thereference voltage V_(ref) 1, then the comparator 3 outputs the signal cwhich gives an instruction to stop the switching operation to thecontrol section 2, and thus the switching section 5 stops the switchingoperation.

[0050] After the switching operation is stopped, the output voltageV_(o) decreases due to power supply to the load, and when the feedbackvoltage V_(fb) 1 becomes lower than the reference voltage V_(ref) 1 by apredetermined value, the comparator 3 outputs the signal c which givesan instruction to start the switching operation to the control section2, and the switching section 5 carries out the switching operationagain. By repeating the foregoing process, the output voltage V_(o) ofthe stabilized power unit 1 comes to be stabilized.

[0051] As described above, according to the stabilized power unit 1 inaccordance with the present embodiment, since the soft start circuit 6is provided, the charged voltage of the output capacitor C3 becomesstabilized within the range of the output voltage V_(o) in steady state,without having an overshoot until the completion of the start-up.Consequently, the stabilized power unit 1 can prevent an overshoot ofthe output voltage V_(o) at the start-up.

[0052] Next, the following examples will explain specific structures ofthe soft start circuit 6 in detail.

EXAMPLE 1

[0053]FIG. 2 shows a stabilized power unit 11 in which a duty adjustmentcircuit 16 is provided as the soft start circuit 6 shown in FIG. 1.Along with this, the integrated portion 1 a in FIG. 1 is illustrated inFIG. 2 as an integrated portion 11 a. The duty adjustment circuit 16 isoperated by using the input voltage V_(in) inputted from the inputterminal T2 as a source voltage. Further, the reference voltage V_(ref)1 of the DC voltage source 4 is inputted to the duty adjustment circuit16, and the duty adjustment circuit 16 outputs a control signal d to thecontrol section 2, using the reference voltage V_(ref) 1. The controlsection 2 controls the switches S1, S2, S3, S4 to carry out theswitching operation so that there is a constant cycle between the startof a charge period and the start of the next charge period. Whenstarting up the stabilized power unit 11, the duty adjustment circuit 16makes the control section 2 gradually increase a duty in the chargeperiod in the foregoing cycle, by the foregoing control signal d. Here,the duty is gradually increased to a predetermined value, that is, sothat the charge period is gradually prolonged to a predetermined value,so as to prevent a rush current from flowing into the voltage-increasingcapacitor C1 at the start-up. Since the rush current is prevented fromflowing into the voltage-increasing capacitor C1, the output capacitorC3 is gradually charged in the voltage-increasing period. This structurecan easily prevent an overshoot of the output voltage V_(o) at thestart-up.

[0054]FIG. 3 shows a structure of the duty adjustment circuit 16. Theduty adjustment circuit 16 in FIG. 3 is a circuit provided with aterminal T161 to which the input voltage V_(in) is inputted via theinput terminal T2, a terminal T162 to which the reference voltageV_(ref) 1 of the DC voltage source 4 is inputted, and a terminal T163from which the control signal d is outputted, and includes in its insidea constant current source I_(p) 1, a capacitor C_(p) 1, a Zener diode 16a, a PWM comparator 16 b, and an oscillator 16 c. Incidentally, it maybe structured that a reference voltage V_(ref) 2 (having the same valueas the reference voltage V_(ref) 1) generated by another DC voltagesource is inputted to the terminal T162, instead of the referencevoltage V_(ref) 1.

[0055] The capacitor C_(p) 1 and the Zener diode 16 a are connected inparallel, and these are connected with the constant current source I_(p)1 in series. The constant current source I_(p) 1 is connected betweenthe terminal T161 and a point p1, and the capacitor C_(p) 1 and theZener diode 16 a are connected between the point p1 and GND lines, witha cathode of the Zener diode 16 a provided on the side of the point p1.The PWM comparator 16 b has two non-reversal input terminals and onereversal input terminal. One of the non-reversal input terminals isconnected to the point p1, the other non-reversal input terminal isconnected to the terminal T162, and the reversal input terminal isconnected to one end of the oscillator 16 c. The other end of theoscillator 16 c is connected to a GND line. Besides, an output terminalof the PWM comparator 16 b is connected to the terminal T163.

[0056] Upon start of the start-up of the stabilized power unit 11, theconstant current source I_(p) 1 generates a constant current from theinput voltage V_(in) inputted from the terminal T161, and flows theconstant current to the point p1. The capacitor C_(p) 1 is charged bythe flowing in of the constant current, and a charge amount is increasedwith time. When the charged voltage of the capacitor C_(p) 1 reachesZener voltage of the Zener diode 16 a, the capacitor C_(p) 1 is notcharged any more, and the constant current flows via the Zener diode 16a. The Zener voltage is set higher than the reference voltage V_(ref) 1.With this structure, a voltage V_(p) 1 between the point p1 and a GNDincreases with time by the inclination of I_(p) 1/C_(p) 1, where I_(p) 1is the constant current and C_(p) 1 is a capacity of the capacitor C_(p)1, and is inputted to one of the non-reversal input terminals of the PWMcomparator 16 b. When the stabilized power unit 11 is stopped, theconstant current source I_(p) 1 stops the generation of the constantcurrent, the capacitor C_(p) 1 gradually discharges via the Zener diode16 a, and the voltage V_(p) 1 returns to an initial value (a GNDpotential). In this manner, the constant current source I_(p) 1 and theZener diode 16 a constitute charge amount changing means for increasingthe charge amount of the capacitor C_(p) 1 with time at the start-up.

[0057] Besides, as shown in a time chart in FIG. 4, the oscillator 16 cgenerates a triangular wave voltage V_(osc) having a predeterminedfrequency, and the PWM comparator 16 b outputs the control signal dwhich gives an instruction to set a period in which the lower voltage ofthe two voltages, the voltage V_(p) 1 and the reference voltage V_(ref)1, is higher than the triangular wave voltage V_(osc) as the chargeperiod, and a period in which the lower voltage is lower than thetriangular wave voltage V_(osc) as the voltage-increasing period, to thecontrol section 2. As shown in FIG. 4, when the voltage V_(p) 1 is lowerthan the reference voltage V_(ref) 1, the period in which the voltageV_(p) 1 is higher than the triangular wave voltage V_(osc) becomeslonger with the increase of the voltage V_(p) 1. Therefore, the chargeperiod in which the switches S1 and S3 are ON and the switches S2 and S4are OFF is gradually prolonged, and the foregoing duty is graduallyincreased. In other words, soft start can be realized. After the voltageV_(p) 1 reaches the reference voltage V_(ref) 1, the reference voltageV_(ref) 1 becomes lower than the voltage V_(p) 1, and the period inwhich the reference voltage V_(ref) 1 is higher than the triangular wavevoltage V_(osc) is constant, therefore the charge period and thevoltage-increasing period become constant. Consequently, by setting thepoint where the voltage V_(p) 1 reaches the reference voltage V_(ref) 1to the point where the start-up is completed, the charge period becomesconstant after the completion of the start-up, and the charge period(duty) in steady state can be obtained. In this manner, the PWMcomparator 16 b determines the charge period and the voltage-increasingperiod at the start-up and in steady state, in accordance with thecharge amount of the capacitor C_(p) 1.

[0058] Consequently, according to the stabilized power unit 11 providedwith the duty adjustment circuit 16 structured as in FIG. 3, the dutyadjustment circuit 16 determines the charge period at the star-up inaccordance with the charge amount of the capacitor C_(p) 1 increasedwith time by the charge amount changing means, and thus the dutyadjustment circuit 16 can easily prevent a rush current from flowinginto the voltage-increasing capacitor C1 at the start up. In addition,it is also possible to provide charge amount changing means fordecreasing the charge amount of a capacitor with time at the start-up,instead of the constant current source I_(p) 1 and the Zener diode 16 a,and to determine the charge period in accordance with the charge amountof the capacitor whose charge amount is decreased with time bydischarge. When using a PWM comparator, it is possible to set a periodin which a voltage height relationship is opposite to the foregoingcase, for example, in which the voltage of the capacitor is higher thanthe reference voltage and lower than the triangular wave voltage (it issatisfactory even when the voltage of the capacitor does not changelinearly with respect to time), as the charge period at the start-up.

[0059] Besides, in the structure shown in FIG. 3, the less theincreasing inclination of the voltage V_(p) 1 is, the more slowly theduty increases, which can provide slower soft start. Since the voltageV_(p) 1 is increased by I_(p) 1/C_(p) 1×t, where t denotes time sincethe capacitor C_(p) 1 is started to be charged by the constant current,the charge period can be adjusted by adjusting the capacity of thecapacitor C_(p) 1. Such a capacitor C_(p) 1 of a desired type may beexternally attached to the integrated portion 11 a, and thus it becomespossible to freely set how to change the charge period at the start-up.

[0060] In such a manner, the charge period is gradually prolonged withtime by the duty adjustment circuit 16 shown in FIG. 3 so as to preventa rush current from flowing into the voltage-increasing capacitor C1 atthe start-up, and the duty adjustment circuit 16 controls the switchingsection 5 at the start-up to carry out the switching operation such thatthe charged voltage of the output capacitor C3 is always not more thanthe output voltage V_(o) in steady state.

[0061] Next, FIG. 5 shows another structure of the duty adjustmentcircuit 16. The members having the same function as those in FIG. 3 willbe designated by the same reference numerals. The duty adjustmentcircuit 16 in FIG. 5 is a circuit provided with the terminals T161,T162, and T163, as in the structure shown in FIG. 3, and includes in itsinside resistors R11, R12, R13, . . . , Rn, the PWM comparator 16 b, theoscillator 16 c, a constant voltage circuit 16 d, a clock countercircuit 16 e, and a switch circuit 16 f.

[0062] The switch circuit 16 f is provided with switches S12, S13, . . ., Sn. The resistor R12 and the switch S12, the resistor R13 and theswitch S13, . . . , and the resistor Rn and the switch Sn make pairsrespectively, and the respective pairs are connected in parallel, withthe resistor and the switch in each pair connected in series. Theresistor side of this parallel circuit is connected with the resistorR11 in series at a point p2. The end of each switch opposite to thepoint connected with the paired resistor is connected with a GND line.The end of the resistor R11 opposite to the point p2 is connected to anoutput terminal of the constant voltage circuit 16 d, and an inputterminal of the constant voltage circuit 16 d is connected to theterminal T161. The point p2 is connected to one of the non-reversalinput terminals of the PWM comparator 16 b. The other non-reversal inputterminal of the PWM comparator 16 b is connected to the terminal T162.An input terminal of the clock counter circuit 16 e is connected to anoutput terminal of the oscillator 16 c, and an output terminal of theclock counter circuit 16 e is connected to a control terminal forswitching ON/OFF the switch circuit 16 f.

[0063] As described in the explanation of FIG. 3, the oscillator 16 coscillates the triangular wave voltage V_(osc) at a predeterminedfrequency, and serves as oscillation means for carrying out oscillationat a predetermined oscillation frequency. The constant voltage circuit16 d generates constant voltage V_(c) 1 from the input voltage V_(in)for output. The clock counter circuit 16 e counts the number oftriangular waves generated by the oscillator 16 c in a digital manner,and serves as counting means for carrying out counting for theoscillation means. Upon start of the start-up of the stabilized powerunit 1, the clock counter circuit 16 e starts counting the number of thetriangular waves generated by the oscillator 16 c, and when the numberof oscillations reaches a predetermined value, the clock counter circuit16 e outputs a signal e giving an instruction which of the switches S12,S13, . . . , Sn should be ON (in connected state), to the switch circuit16 f. In other words, the clock counter circuit 16 e detects the passageof time by counting the number of oscillations. The switch circuit 16 freceives the signal e from the clock counter circuit 16 e, and switchesON only the switch corresponding to the signal e among the switches S12,S13, . . . , Sn. A voltage V_(p) 2 between the point p2 and a GNDbecomes a divided voltage of the constant voltage V_(c) 1 determined bythe resistor connected with the switch which becomes ON in series andthe resistor R11, and is inputted to the PWM comparator 16 b.

[0064] As shown in a time chart in FIG. 6, at the start-up, the switchcircuit 16 f switches ON a predetermined switch (for example, the switchS12) so that the voltage V_(p) 2 becomes lowest. The clock countercircuit 16 e counts the number of the triangular waves generated by theoscillator 16 c, and outputs the signal e, by which the initial switchON state can be maintained, to the switch circuit 16 f until the countreaches the first threshold. When the count reaches the first threshold,the clock counter circuit 16 e outputs the signal e, which switches ONonly a switch (for example, switch S13) which makes the voltage V_(p) 2the second lowest, to the switch circuit 16 f. In such a manner, theswitches are switched for each threshold for the count, so as toincrease the value of the voltage V_(p) 2 step by step.

[0065] The PWM comparator 16 b compares the voltage V_(p) 2 with thereference voltage V_(ref) 1, and outputs the signal d to the controlsection 2 so that the period in which the lower voltage of the twobecomes higher than the triangular wave voltage V_(osc) comes to be thecharge period in which the switches S1 and S3 are ON and the switches S2and S4 are OFF, and that the period in which the lower voltage of thetwo becomes lower than the triangular wave voltage V_(osc) comes to bethe voltage-increasing period in which the switches S1 and S3 are OFFand the switches S2 and S4 are ON. Since the voltage V_(p) 2 is setlower than the reference voltage V_(ref) 1 at the start-up, the chargeperiod (duty) becomes longer with time. When the voltage V_(p) 2 reachesthe reference voltage V_(ref) 1, the charge period and thevoltage-increasing period become constant afterwards. In addition, thevoltage V_(p) 2 is set to be changed little by little by the switchingoperation of the switches in the switch circuit 16 f, so that the chargeperiod is gradually prolonged to the foregoing constant predeterminedvalue so as to prevent a rush current from flowing into thevoltage-increasing capacitor C1.

[0066] In this manner, according to the duty adjustment circuit 16structured as shown in FIG. 5, the clock counter circuit 16 e counts thenumber of oscillations of the oscillator 16 c at the start-up so as todetect the passage of time, and the charge period is determined based onthe detected passage of time. Therefore, it becomes possible to easilyprevent a rush current from flowing into the voltage-increasingcapacitor C1 at the start-up.

[0067] Thus, the charge period is gradually prolonged with time by theduty adjustment circuit 16 shown in FIG. 5 so as to prevent a rushcurrent from flowing into the voltage-increasing capacitor C1 at thestart-up, and the duty adjustment circuit 16 controls the switchingsection 5 at the start-up to carry out the switching operation such thatthe charged voltage of the output capacitor C3 is always not more thanthe output voltage V_(o) in steady state.

EXAMPLE 2

[0068]FIG. 7 shows a stabilized power unit 21 in which an oscillationfrequency adjustment circuit 26 is provided as the soft start circuit 6shown in FIG. 1. Along with this, the integrated portion 1 a in FIG. 1is illustrated in FIG. 7 as an integrated portion 21 a. The oscillationfrequency adjustment circuit 26 is operated by using the input voltageV_(in) inputted from the input terminal T2 as a source voltage, andoutputs a control signal f to the control section 2. At the start-up ofthe stabilized power unit 21, the oscillation frequency adjustmentcircuit 26 makes the control section 2 gradually prolong the chargeperiod, by the foregoing control signal f. Besides, the charge period isincreased so as to be gradually prolonged to a predetermined value inorder to prevent a rush current from flowing into the voltage-increasingcapacitor C1 at the start-up. Since the rush current is prevented fromflowing into the voltage-increasing capacitor C1, the output capacitorC3 is gradually charged in the voltage-increasing period. This structurecan easily prevent an overshoot of the output voltage V_(o) at thestart-up.

[0069]FIG. 8 shows a structure of the oscillation frequency adjustmentcircuit 26. The oscillation frequency adjustment circuit 26 in FIG. 8 isa circuit provided with a terminal T261 to which the input voltageV_(in) is inputted via the input terminal T2, a terminal T262 to which areference voltage V_(ref) 3 of a DC voltage source (not shown) providedtogether with the oscillation frequency adjustment circuit 26 isinputted, and a terminal T263 from which the control signal f isoutputted, and includes a constant current source I_(p) 3, a capacitorC_(p) 3, resistors r1 and r2, a Zener diode 26 a, comparators 26 b and26 c, and an oscillator 26 d.

[0070] The capacitor C_(p) 3 and the Zener diode 26 a are connected inparallel, and these are connected with the constant current source I_(p)3 in series. The constant current source I_(p) 3 is connected betweenthe terminal T261 and a point p3, and the capacitor C_(p) 3 and theZener diode 26 a are connected between the point p3 and GND lines, witha cathode of the Zener diode 26 a provided on the side of the point p3.The comparator 26 b has one non-reversal input terminal and one reversalinput terminal, and the non-reversal input terminal is connected to thepoint p3. The resistors r1 and r2 are connected in series between theterminal T262 and a GND line, with the resistor r2 provided on the sideof the GND, and the reversal input terminal of the comparator 26 b isconnected to a connecting point between the resistors r1 and r2.Besides, an output terminal of the comparator 26 b is connected to aninput terminal of the oscillator 26 d. The comparator 26 c has onenon-reversal input terminal and one reversal input terminal, and thenon-reversal input terminal is connected to the terminal T262, and thereversal input terminal is connected to an output terminal of theoscillator 26 d. An output terminal of the comparator 26 c is connectedto the terminal T263.

[0071] Upon start of the start-up of the stabilized power unit 21, theconstant current source I_(p) 3 generates a constant current from theinput voltage V_(in) inputted from the terminal T261, and flows theconstant current to the point p3. The capacitor C_(p) 3 is charged bythe flowing in of the constant current, and its charge amount isincreased with time. When the charged voltage of the capacitor C_(p) 3reaches Zener voltage of the Zener diode 26 a, the capacitor C_(p) 3 isnot charged any more, and the constant current flows via the Zener diode26 a. The Zener voltage is set higher than a reference voltage V_(ref)4. With this structure, a voltage V_(p) 3 between the point p3 and a GNDincreases with time, and is inputted to the non-reversal input terminalof the comparator 26 b. When the stabilized power unit 21 is stopped,the constant current source I_(p) 3 stops the generation of the constantcurrent, the capacitor C_(p) 3 gradually discharges via the Zener diode26 a, and the voltage V_(p) 3 returns to an initial value (a GNDpotential).

[0072] To the reversal input terminal of the comparator 26 b is inputtedthe reference voltage V_(ref) 4 which is a divided voltage of thereference voltage V_(ref) 3 generated by the resistors r1 and r2, andthe comparator 26 b compares the voltage V_(p) 3 inputted to thenon-reversal input terminal with the reference voltage V_(ref) 4. Theoscillator 26 d is an oscillation-frequency-changeable oscillator forgenerating the triangular wave voltage V_(osc), and the comparator 26 boutputs a signal g for changing the oscillation frequency of theoscillator 26 d to the oscillator 26 d, based on the voltage heightrelationship between the voltage V_(p) 3 and the reference voltageV_(ref) 4. Here, at the start-up of the stabilized power unit 21, thecomparator 26 b outputs the signal g so as to make the oscillator 26 dto carry out oscillation at the highest oscillation frequency duringwhen the voltage V_(p) 3 is lower than the reference voltage V_(ref) 4,and so as to make the oscillator 26 d to carry out oscillation at thesecond highest oscillation frequency when the voltage V_(p) 3 increasesand reaches the reference voltage V_(ref) 4. By increasing the types ofthe signal g, the comparator 26 b can switch oscillation frequencies ofthe oscillator 26 d to lower ones one by one. In this manner, theconstant current source I_(p) 3, the capacitor C_(p) 3, the resistors r1and r2, the Zener diode 26 a, the comparator 26 b, and the oscillator 26d constitute oscillation means for carrying out oscillation with theoscillation frequency changed from high to low with time at thestart-up. Besides, the constant current source I_(p) 3 and the Zenerdiode 26 a constitute charge amount changing means for increasing ordecreasing the charge amount of the capacitor C_(p) 3 with time at thestart-up.

[0073] The comparator 26 c compares the reference voltage V_(ref) 3inputted to the non-reversal input terminal with the triangular wavevoltage V_(osc) inputted to the reversal input terminal, and outputs thecontrol signal f in accordance with the voltage height relationshipbetween the two voltages. Here, as shown in a time chart in FIG. 9, whenthe reference voltage V_(ref) 3 is higher than the triangular wavevoltage V_(osc), the comparator 26 c outputs the control signal f whichgives an instruction to set the period as the charge period in which theswitches S1 and S3 are ON and the switches S2 and S4 are OFF, to thecontrol section 2. On the other hand, when the reference voltage V_(ref)3 is lower than the triangular wave voltage V_(osc), the comparator 26 coutputs the control signal f which gives an instruction to set theperiod as the voltage-increasing period in which the switches S1 and S3are OFF and the switches S2 and S4 are ON, to the control section 2.

[0074] As shown in FIG. 9, as the oscillation frequency of theoscillator 26 d becomes lower in such a manner that, after the start ofthe start-up, the capacitor C_(p) 3 is being charged, and when thevoltage V_(p) 3 reaches the reference voltage V_(ref) 4, the frequencyof the triangular wave voltage V_(osc) becomes lower, the period inwhich the reference voltage V_(ref) 3 is higher than the triangular wavevoltage V_(osc) is gradually prolonged, and thus the charge period isgradually prolonged. After the completion of the start-up, theoscillation frequency of the oscillator 26 d becomes constant.

[0075] In this manner, the oscillation frequency adjustment circuit 26structured as shown in FIG. 8 includes the above-mentioned oscillationmeans, and determines the charge period at the start-up based on theoscillation frequency. Since the charge period at the start-up isdetermined based on the oscillation frequency of the oscillation meanswhich carries out oscillation with varying with time from a highfrequency to a low frequency, it becomes possible to easily prevent arush current from flowing into the voltage-increasing capacitor C1 atthe start-up.

[0076] In addition, since the oscillation frequency of the oscillationmeans at the start-up is changed based on the charge amount of thecapacitor C_(p) 3 whose charge amount is increased with time by thecharge amount changing means, it becomes possible to prevent a rushcurrent from flowing into the voltage-increasing capacitor C1 at thestart-up more easily. Incidentally, as in Example 1, it is possible toprovide charge amount changing means for decreasing the charge amount ofa capacitor with time at the start-up, instead of the constant currentsource I_(p) 3 and the Zener diode 26 a.

[0077] Besides, in the structure shown in FIG. 8, the less theincreasing inclination of the voltage V_(p) 3 is, the longer theinterval of the timing that the oscillation frequency of the oscillator26 d switches from a high frequency to a low frequency is, which canprovide slower soft start. Since the voltage V_(p) 3 is increased byI_(p) 3/C_(p) 3×t, where t denotes time since the capacitor C_(p) 3 isstarted to be charged by the constant current, the charge period can beadjusted by adjusting the capacity of the capacitor C_(p) 3. Such acapacitor C_(p) 3 of a desired type may be externally attached to theintegrated portion 21 a, and thus it becomes possible to freely set howto change the charge period at the start-up.

[0078] In such a manner, the charge period is gradually prolonged withtime by the oscillation frequency adjustment circuit 26 shown in FIG. 8so as to prevent a rush current from flowing into the voltage-increasingcapacitor C1 at the start-up, and the oscillation frequency adjustmentcircuit 26 controls the switching section 5 at the start-up to carry outthe switching operation such that the charged voltage of the outputcapacitor C3 is always not more than the output voltage V_(o) in steadystate.

[0079] Next, FIG. 10 shows another structure of the oscillationfrequency adjustment circuit 26. The oscillation frequency adjustmentcircuit 26 in FIG. 10 is a circuit which is provided with the terminalT263 from which the control signal f is outputted, and a terminal T264to which a reference voltage V_(ref) 5 of a DC voltage source (notshown) provided together with the oscillation frequency adjustmentcircuit 26 is inputted, but which does not have a terminal to which theinput voltage V_(in) is inputted, and includes an oscillator 26 d, acomparator 26 e, and a clock counter circuit 26 f. The comparator 26 ehas one non-reversal input terminal and one reversal input terminal: thenon-reversal input terminal is connected to the terminal T264, and thereversal input terminal is connected to an output terminal of theoscillator 26 d. An input terminal of the clock counter circuit 26 f isconnected to an output terminal of the oscillator 26 d, and an outputterminal of the clock counter circuit 26 f is connected to anoscillation frequency control terminal of the oscillator 26 d. An outputterminal of the comparator 26 e is connected to the terminal T263.

[0080] The comparator 26 e compares the reference voltage V_(ref) 5inputted to the non-reversal input terminal with the triangular wavevoltage V_(osc) of the oscillator 26 d inputted to the reversal inputterminal, and outputs the control signal f in accordance with thevoltage height relationship between the reference voltage V_(ref) 5 andthe triangular wave voltage V_(osc). The control signal f is structuredthe same as the one used in the oscillation frequency adjustment circuit26 shown in FIG. 8. The clock counter circuit 26 f counts the number ofoscillations of a triangular wave outputted from the oscillator 26 d,and outputs a signal h for changing the oscillation frequency of theoscillator 26 d from a high frequency to a low frequency, to theoscillator 26 d, whenever the count reaches a predetermined threshold.Thus, soft start as shown in the time chart in FIG. 9 can be realized.

[0081] In this manner, the oscillator 26 d and the clock counter circuit26 f constitute oscillation means for carrying out oscillation with theoscillation frequency changed from high to low with time at thestart-up. Besides, the clock counter circuit 26 f serves as countingmeans for counting the number of oscillations of the oscillation means.Since the oscillation frequency adjustment circuit 26 shown in FIG. 10detects the passage of time by counting the number of oscillations ofthe oscillation means at the start-up by the counting means, and changesthe oscillation frequency of the oscillation means based on the detectedpassage of time, it becomes possible to prevent a rush current fromflowing into the voltage-increasing capacitor C1 at the start-up moreeasily.

[0082] In such a manner, the charge period is gradually prolonged withtime by the oscillation frequency adjustment circuit 26 shown in FIG. 10so as to prevent a rush current from flowing into the voltage-increasingcapacitor C1 at the start-up, and the oscillation frequency adjustmentcircuit 26 controls the switching section 5 at the start-up to carry outthe switching operation such that the charged voltage of the outputcapacitor C3 is always not more than the output voltage V_(o) in steadystate.

EXAMPLE 3

[0083]FIG. 11 shows a stabilized power unit 31 in which a gate voltageadjustment circuit 36 is provided as the soft start circuit 6 shown inFIG. 1. Along with this, the integrated portion 1 a in FIG. 1 isillustrated in FIG. 11 as an integrated portion 31 a. Besides, each ofthe switches S1 and S3 is a first switch for connecting a path forcharging the voltage-increasing capacitor C1 in the charge period, andfor cutting off the path for charging the voltage-increasing capacitorC1 in the voltage-increasing period, and at least one of the switches S1and S3 is constituted by a field-effect transistor (hereinafter referredto as a MOSFET).

[0084] The gate voltage adjustment circuit 36 is operated by using theinput voltage V_(in) inputted from the input terminal T2 as a sourcevoltage, and controls the switching section 5 (see FIG. 1) by adjustingthe signal a outputted from the control section 2 for operating theMOSFET, that is, the signal for supplying a gate voltage for the MOSFET,so as to be a signal a′. More specifically, at the start-up, in order toprevent a rush current from flowing in the output capacitor C3 in thevoltage-increasing period, a channel resistance when the MOSFET isconducting, here, in the charge period, is gradually decreased from ahigher value by adjusting the gate voltage, so as to gradually increasea final charged voltage charged to the voltage-increasing capacitor C1in the respective charge periods having an identical length, with thepassage of time since the start of the start-up. Here, suppose that thesignal b is not adjusted. In this manner, the gate voltage adjustmentcircuit 36 controls the switching section 5 to carry out the switchingoperation so as to exercise channel resistance control for decreasingthe channel resistance with time when at least one MOSFET is conducting,for the purpose of preventing a rush current from flowing into theoutput capacitor C3 at the start-up.

[0085] Through the control of the gate voltage adjustment circuit 36 onthe switching section 5, the output capacitor C3 is gradually charged atthe start-up. Consequently, this structure can easily prevent anovershoot of the output voltage V_(o) at the start-up. Besides, since norush current flows, the current rating of the MOSFET can be set lower.

[0086] Incidentally, in the foregoing example, at least one of theswitches S1 and S3 is defined as a MOSFET, but the present invention isnot limited to this. Each of the switches S2 and S4 is a second switchfor cutting off a path for charging the output capacitor C3 in thecharge period, and for connecting the path for charging the outputcapacitor C3 in the voltage-increasing period, and it is satisfactorythat at least one of the first switch and the second switch, or at leastone of the switches S1, S2, S3, S4 in the present embodiment, is aMOSFET. The MOSFET provided as the second switch prevents a currentflowing into the output capacitor C3 in each voltage-increasing periodfrom becoming a rush current directly.

[0087]FIG. 12 shows a structure of the gate voltage adjustment circuit36. The gate voltage adjustment circuit 36 in FIG. 12 is structured forthe switch S1 in FIG. 11. The gate voltage adjustment circuit 36 is acircuit provided with a terminal T361 to which the input voltage V_(in)is inputted via the input terminal T2, a terminal T362 connected to aGND line, a terminal T363 to which the signal a is inputted from thecontrol section 2, and a terminal T364 from which the signal a′ isoutputted, and includes a constant voltage circuit 36 a, a capacitorC_(p) 4, a resistor r3, and switching elements S36 and S36′. Besides,suppose that the switch S1 is a p-channel MOSFET.

[0088] The constant voltage circuit 36 a are connected to the terminalsT361 and T362 which serve as power terminals. Between an output terminalof the constant voltage circuit 36 a and a GND line, the capacitor C_(p)4 and the resistor r3 are connected in series via a point p4, with theresistor r3 provided on the side of a GND. The switching element S36 isconnected between the point 4 and the terminal T364, and a controlterminal for switching ON and OFF the switching element S36 is connectedto the terminal T363. The switching element S36′ is connected betweenthe terminal T361 and the terminal T364, and a control terminal forswitching ON and OFF the switching element S36′ is connected to theterminal T363. The switching element S36 is ON when the signal ainputted from the control section 2 via the terminal T363 is in a “LOW”level, and is OFF when the signal a is in a “HIGH” level. The switchingelement S36′ is ON when the signal a is in a “HIGH” level, and is OFFwhen the signal a is in a “LOW” level.

[0089] Before the stabilized power unit 31 is started up, the switchingelement 36′ is ON, and the MOSFET is OFF as a source and a gate of theMOSFET are short-circuited. Upon start of the start-up of the stabilizedpower unit 31, the constant voltage circuit 36 a generates a constantvoltage V_(c) 2 from the input voltage V_(in) for output. The capacitorC_(p) 4 is gradually charged by the application of the constant voltageV_(c) 2 to a circuit in which the capacitor C_(p) 4 and the resistor r3are connected in series. In the charge period, the signal a becomes“LOW”, which makes the switching element S36 ON and thus the point p4and the terminal T364 are short-circuited, and which makes the switchingelement S36′ OFF and thus a short-circuit path between the terminal T361and the terminal 364 is cut off. In the voltage-increasing period, thesignal a becomes “HIGH”, which makes the switching element S36 OFF andthus a short-circuit path between the point p4 and the terminal T364 iscut off. With this structure, in the charge period, signal a′ having avoltage V_(p) 4 between the point 4 and the terminal T364 is outputtedfrom the terminal T364 to the switch S1, and a gate voltage within arange which makes the switch S1 ON is applied.

[0090] As shown in a time chart in FIG. 13, the voltage V_(p) 4 declinesfrom the voltage V_(c) 2 with a time constant determined by thecapacitor C_(p) 4 and the resistor r3. Therefore, even whenpredetermined, constant charge period and voltage-increasing period arerepeated, the channel resistance of the MOSFET in the charge perioddecreases with time, and in steady state reached after a sufficientpassage of time, the voltage V_(p) 4 becomes virtually zero and thechannel resistance is minimized. Consequently, in an initial stage ofthe start-up where the channel resistance is high, thevoltage-increasing capacitor C1 is gradually charged in the chargeperiod and the output capacitor C3 is also gradually charged, and as thechannel resistance decreases, the charge amount in the charge period isincreased, and the charged voltage of the output capacitor C3 is alsoincreased. After the operation of the stabilized power unit 31 isstopped, the operation of the constant voltage circuit 36 a is alsostopped, and the accumulated charge in the capacitor C_(p) 4 isdischarged.

[0091] In this manner, the constant voltage circuit 36 a and theresistor r3 constitute charge amount changing means for increasing thecharge amount of the capacitor C_(p) 4 with time at the start-up. Thegate voltage adjustment circuit 36 decreases the channel resistance in aperiod for charging the MOSFET at the start-up, that is, in a period inwhich the MOSFET is conducting, based on the charge amount of thecapacitor C_(p) 4 which is increased with time at the start-up, and thusit can easily prevent a rush current from flowing into the outputcapacitor C3 at the start-up. In this manner, the channel resistancewhen the MOSFET is conducting is gradually decreased with time so as toprevent a rush current from flowing into the output capacitor C3 at thestart-up, and the gate voltage adjustment circuit 36 controls theswitching section 5 at the start-up to carry out the switching operationsuch that the charged voltage of the output capacitor C3 is always notmore than the output voltage V_(o) in steady state.

[0092] Such a capacitor C_(p) 4 of a desired type may be externallyattached, and thus it becomes possible to freely set how to decrease thechannel resistance of the MOSFET in the charge period at the start-up.Incidentally, it is also possible to provide charge amount changingmeans for decreasing the charge amount of the capacitor C_(p) 4 withtime at the start-up, so as to decrease the channel resistance of theMOSFET in the charge period at the start-up based on the charge amountof the capacitor C_(p) 4 which is increased with time.

[0093] Next, FIG. 14 shows another structure of the gate voltageadjustment circuit 36. The gate voltage adjustment circuit 36 in FIG. 14is structured for the switch S1 in FIG. 11, and as in the gate voltageadjustment circuit 36 in FIG. 12, it is a circuit provided with theterminals T361 to T364, and includes a constant voltage circuit 36 b, aclock counter circuit 36 c, a switch circuit 36 d, resistors r31, r32,r33, . . . , rn, and the switching elements S36 and S36′.

[0094] The constant voltage circuit 36 b are connected to the terminalsT361 and T362 which serve as power terminals. The switch circuit 36 dincludes switches s32, s33, . . . , sn. The resistor r32 and the switchs32, the resistor r33 and the switch s33, . . . , and the resistor rnand the switch sn make pairs respectively, and the respective pairs areconnected in parallel, with the resistor and the switch in each pairconnected in series. The resistor side of this parallel circuit isconnected with the resistor r31 in series at a point p5. The resistancevalues of the resistors r32, r33, . . . , rn are set such that theresistor r32 has the greatest resistance value, the resistor r33 has thesecond greatest resistance value, and the resistance values of theresistors afterwards gradually decrease, whereas the resistance value ofthe resistor rn is zero. The end of each switch opposite to the pointconnected with the paired resistor is connected with a GND line. The endof the resistor r31 opposite to the point p5 is connected to an outputterminal of the constant voltage circuit 36 b. An input terminal of theclock counter circuit 36 c is connected to the terminal T363, and anoutput terminal of the clock counter circuit 36 c is connected to acontrol terminal for switching ON/OFF the switch circuit 36 d. Theswitching element S36 is connected between the point p5 and the terminalT364, and a control terminal for switching ON/OFF the switching elementS36 is connected to the terminal T363. The switching element S36′ isconnected in the same way as in FIG. 12.

[0095] Before the stabilized power unit 31 is started up, the switchingelement 36′ is ON, and the MOSFET is OFF as a source and a gate of theMOSFET are short-circuited. Upon start of the start-up of the stabilizedpower unit 31, the constant voltage circuit 36 b generates a constantvoltage V_(c) 3 from the input voltage V_(in) for output. The signal ainputted from the terminal T363 after the start-up of the stabilizedpower unit 31 is started is originally a switching signal constituted bya pulse corresponding to the switching operation, together with thesignal b. The clock counter circuit 36 c counts the number of pulses ofthe signal a, and whenever the count reaches a predetermined threshold,the clock counter circuit 36 c outputs a signal i which gives aninstruction to switch ON (close) only one switch corresponding to eachthreshold, to the switch circuit 36 d. With this structure, a voltageV_(p) 5 is generated by dividing the voltage V_(c) 3, at the point p5.In the charge period, the signal a becomes “LOW”, which makes theswitching element S36 ON (connected state) and the switching elementS36′ OFF (cut-off state), and the voltage V_(p) 5 is outputted from theterminal T364 as a voltage of the signal a′, that is, the gate voltageof the MOSFET. On the other hand, in the voltage-increasing period, thesignal a becomes “HIGH”, which makes the switching element S36 OFF andthe switching element S36′ ON, and the MOSFET becomes OFF with thesource and the gate short-circuited.

[0096] As shown in a time chart in shown FIG. 15, when the start-up ofthe stabilized power unit 31 is started, the switch s32 of the switchcircuit S36 d is ON so that the voltage V_(p) 5 has the greatest valueV_(c), and whenever the count of the number of pulses of the signal acounted by the clock counter circuit 36 c reaches a threshold (for eachincrement in FIG. 15), the switch in the switch circuit 36 d is switchedin order of s32→s33→ . . . →sn, and the voltage V_(p) 5 is reduced stepby step. At the completion of the start-up, the switch sn is closed andthe voltage V_(p) 5 becomes zero. Consequently, in order to prevent arush current from flowing into the output capacitor C3, the channelresistance of the MOSFET is decreased with time in the charge period,and the output capacitor C3 is gradually charged in thevoltage-increasing period.

[0097] In this manner, the control section 2 serves as switching signalgeneration means for generating the switching signal, and the clockcounter circuit 36 c serves as counting means for counting the number ofpulses of the switching signal generated by the switching signalgeneration means. Since the gate voltage adjustment circuit 36 detectsthe passage of time at the start-up by counting the number of pulses ofthe signal a by means of the clock counter circuit 36 c, and reduces thechannel resistance when the MOSFET is conducting based on the detectedpassage of time, it becomes possible to easily prevent a rush currentfrom flowing into the output capacitor C3 at the start-up. In such amanner, the channel resistance when the MOSFET is conducting isgradually reduced with time so as to prevent a rush current from flowinginto the output capacitor C3 at the start-up, and the gate voltageadjustment circuit 36 controls the switching section 5 at the start-upto carry out the switching operation such that the charged voltage ofthe output capacitor C3 is always not more than the output voltage V_(o)in steady state. Incidentally, in FIGS. 12 and 14, it is satisfactorythat the signal a is a signal generated corresponding to the switchingoperation of the switch S1, and its HIGH/LOW level may be reversedcompared with the foregoing example as long as the ON/OFF relationshipof the switches S36 and S36′ is the same as in the foregoing example.

EXAMPLE 4

[0098]FIG. 16 shows a stabilized power unit 41 in which a referencevoltage adjustment circuit 46 is provided as the soft start circuit 6shown in FIG. 1. Along with this, the integrated portion 1 a in FIG. 1is illustrated in FIG. 16 as an integrated portion 41 a. Besides, thedirect voltage source 4 in FIG. 1 is deleted, and suppose that thereference voltage adjustment circuit 46 is a voltage source whichoperates using the input voltage V_(in) as a source voltage, andgenerates a reference voltage V_(ref) 6 so as to be voltage-adjustableand inputs the reference voltage V_(ref) 6 to a reversal input terminalof the comparator 3. In other words, the reference voltage adjustmentcircuit 46 serves as a part of the switching section 5.

[0099] Upon start of the start-up of the stabilized power unit 41, thereference voltage adjustment circuit 46 increases the reference voltageV_(ref) 6 to a predetermined value in steady state. The comparator 3compares the feedback voltage V_(fb) 1, which is the detected value ofthe output voltage V_(o) detected by the voltage-dividing resistors R1and R2, with the reference voltage V_(ref) 6. When the feedback voltageV_(fb) 1 reaches the reference voltage V_(ref) 6 during the switchingoperation, the reference voltage adjustment circuit 46 outputs thesignal c which gives an instruction to stop the switching operation in acondition that a charge from the voltage-increasing capacitor C1 to theoutput capacitor C3 is not carried out, to the control section 2. On theother hand, when the feedback voltage V_(fb) 1 decreases by apredetermined value while the switching operation is stopped, thereference voltage adjustment circuit 46 outputs the signal c which givesan instruction to carry out the switching operation, to the controlsection 2.

[0100] In this manner, the voltage-dividing resistors R1 and R2 serve asoutput voltage detection means for detecting the output voltage V_(o).Besides, the reference voltage adjustment circuit 46 also serves asreference voltage generation means for generating the reference voltageV_(ref) 6 so as to be voltage-adjustable. Further, the comparator 3serves as comparison means which compares the detected value of theoutput voltage V_(o) detected by the voltage-dividing resistors R1 andR2 (the feedback voltage V_(fb) 1) with the reference voltage V_(ref) 6,and stops the switching operation in a condition that a charge from thevoltage-increasing capacitor C1 to the output capacitor C3 is notcarried out when the detected value becomes not less than the referencevoltage V_(ref) 6 during the switching operation, and makes theswitching section 5 to carry out the switching operation when thedetected value decreases by a predetermined value while the switchingoperation is stopped.

[0101] The reference voltage adjustment circuit 46 increases thereference voltage V_(ref) 6 to a predetermined value so as to prevent arush current from flowing into the voltage-increasing capacitor C1 atthe start-up. With this structure, the output capacitor C3 is graduallycharged in the voltage-increasing period. Therefore, this structure caneasily prevent an overshoot of the output voltage V_(o) at the start-up.Besides, since the structure by which the reference voltage adjustmentcircuit 46 increases the reference voltage V_(ref) 6 can be designedvery easily, complicated processes are not required and a chip area canbe reduced when the structure is made up in a chip, and thus a softstart function can be attached inexpensively.

[0102] Next, FIG. 17 shows a structure of the reference voltageadjustment circuit 46. The reference voltage adjustment circuit 46 isprovided with a terminal T461 to which the input voltage V_(in) isinputted via the input terminal T2, and a terminal T462 for outputtingthe reference voltage V_(ref) 6, and includes a constant voltage circuit46 a, resistors rc1 and rc2, and a capacitor C46. The resistors rc1 andrc2 are connected in series between the constant voltage circuit 46 aand a GND line, with the resistor rc2 provided on the side of a GND. Theconstant voltage circuit 46 a is connected between the terminal T461 andan end of the resistor rc1 opposite to the point connected with theresistor rc2. The point connecting the resistors rcl and rc2 isconnected to the terminal T462, and the capacitor C46 is connectedbetween the terminal T462 and a GND line.

[0103] Upon start of the start-up of the stabilized power unit 41, theconstant voltage circuit 46 a generates a constant voltage V_(c) 4 fromthe input voltage V_(in) for output. By the output of the voltage V_(c)4, a current flows into the resistors rc1 and rc2, and the capacitor C46becomes charged. With this arrangement, a voltage between the terminalsof the capacitor C46, determined according to element constants of theresistors rc1 and rc2 and the capacitor C46, is outputted from theterminal T462 as the reference voltage V_(ref) 6, so as to be graduallyincreased as shown in a time chart in FIG. 18. When the feedback voltageV_(fb) 1 is lower than the reference voltage V_(ref) 6, the switchingoperation is continued (ON) and the feedback voltage V_(fb) 1 isgradually increased, and when the feedback voltage V_(fb) 1 reaches thereference voltage V_(ref) 6, the switching operation is stopped (OFF).When the feedback voltage V_(fb) 1 is declined by a predeterminedvoltage while the switching operation is stopped, the switchingoperation is started again, and the feedback voltage V_(fb) 1 isapproaching a value in steady state, with some up-and-down movements.

[0104] In this manner, the constant voltage circuit 46 a and theresistors rc1 and rc2 constitute charge amount changing means forincreasing or decreasing the charge amount of the capacitor C46 withtime at the start-up. Since the reference voltage adjustment circuit 46increases the reference voltage V_(ref) 6 at the start-up based on thecharge amount of the capacitor C46 increased or decreased with time, itbecomes possible to easily prevent a rush current from flowing into thevoltage-increasing capacitor C1. Besides, such a capacitor C46 of adesired type may be externally attached, and thus it becomes possible tofreely set how to increase the reference voltage by the referencevoltage adjustment circuit 46 at the start-up.

[0105] In such a manner, the switching operation is carried out by thereference voltage adjustment circuit 46 shown in FIG. 17 so as toprevent a rush current from flowing into the voltage-increasingcapacitor C1 at the start-up, and the reference voltage adjustmentcircuit 46 controls the switching section 5 at the start-up to carry outthe switching operation such that the charged voltage of the outputcapacitor C3 is always not more than the output voltage V_(o) in steadystate.

[0106] As described, a stabilized power unit of the present invention isa switched-capacitor-type stabilized power unit structured so as toinclude:

[0107] an voltage-increasing capacitor which is charged based on aninput voltage and whose voltage is increased after being charged;

[0108] switching means for carrying out switching operation toalternately switch a charge period and a voltage-increasing period ofthe voltage-increasing capacitor; and

[0109] an output capacitor which outputs a charged voltage obtained bybeing charged utilizing a voltage-increasing potential of thevoltage-increasing capacitor in the voltage-increasing period, as anoutput voltage, and stabilizes the charged voltage within a range of theoutput voltage in steady state through a plurality of thevoltage-increasing periods after a start-up is started,

[0110] wherein the stabilized power unit includes soft start means forcontrolling the switching means to carry out the switching operation sothat the charged voltage always becomes not more than the output voltagein the steady state, at the start-up from when the start-up is starteduntil when the charged voltage is stabilized within the range of theoutput voltage in the steady state.

[0111] According to the foregoing invention, at the start-up, the softstart means controls the switching means to carry out the switchingoperation so that the charged voltage of the output capacitor alwaysbecomes not more than the output voltage in the steady state. With thisstructure, the charged voltage of the output capacitor becomesstabilized within the range of the output voltage in the steady state,without having an overshoot until the completion of the start-up.Consequently, it becomes possible to provide a switched-capacitor-typestabilized power unit which can prevent an overshoot of the outputvoltage at the start-up, in the structure having the output capacitorwhich outputs the charged voltage obtained through a plurality ofcharges by the switching operation utilizing a voltage-increasingpotential of the voltage-increasing capacitor, as an output voltage.

[0112] The stabilized power unit of the present invention may bestructured such that:

[0113] the soft start means controls the switching means so as to carryout the switching operation so that the charge period is graduallyprolonged to a predetermined value, so as to prevent a rush current fromflowing into the voltage-increasing capacitor at the start-up.

[0114] According to the foregoing invention, under the control of thesoft start means, the switching means carries out the switchingoperation so that the charge period is gradually prolonged to thepredetermined value at the start-up, and prevents a rush current fromflowing into the voltage-increasing capacitor. Therefore, the outputcapacitor is gradually charged in the voltage-increasing period.Consequently, it becomes possible to easily prevent an overshoot of theoutput voltage at the start-up.

[0115] The stabilized power unit may be structured such that:

[0116] the soft start means includes a capacitor and charge amountchanging means for increasing or decreasing a charge amount of thecapacitor with time at the start-up; and

[0117] the soft start means determines the charge period at the start-upbased on the charge amount of the capacitor.

[0118] According to the foregoing invention, since the soft start meansdetermines the charge period at the start-up based on the charge amountof the capacitor which is increased or decreased with time by the chargeamount changing means, it becomes possible to easily prevent a rushcurrent from flowing into the voltage-increasing capacitor at thestart-up. Besides, since the capacitor of a desired type may beexternally attached, it becomes possible to freely set how to change thecharge period at the start-up.

[0119] Further, the stabilized power unit of the present invention maybe structured such that:

[0120] the soft start means includes oscillation means for carrying outoscillation at a predetermined oscillation frequency and counting meansfor counting the number of oscillations of the oscillation means; and

[0121] the soft start means detects a passage of time by counting thenumber of the oscillations by the counting means at the start-up, anddetermines the charge period based on a detection result of the passageof time.

[0122] According to the foregoing invention, since the soft start meansdetects the passage of time by counting the number of the oscillationsof the oscillation means by the counting means at the start-up, anddetermines the charge period based on the detection result of thepassage of time, it becomes possible to easily prevent a rush currentfrom flowing into the voltage-increasing capacitor at the start-up.

[0123] Further, to achieve the foregoing object, the stabilized powerunit may be structured such that:

[0124] the soft start means includes oscillation means for carrying outoscillation with an oscillation frequency changed from high to low withtime at the start-up; and

[0125] the soft start means determines the charge period at thestart-up, based on the oscillation frequency.

[0126] According to the foregoing invention, the soft start meansdetermines the charge period at the start up based on the oscillationfrequency of the oscillation means for carrying out oscillation, theoscillation frequency being changed from high to low with time.Consequently, it becomes possible to easily prevent a rush current fromflowing into the voltage-increasing capacitor at the start-up.

[0127] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0128] the soft start means includes a capacitor and charge amountchanging means for increasing or decreasing a charge amount of thecapacitor with time at the start-up; and

[0129] the soft start means changes the oscillation frequency at thestart-up, based on the charge amount of the capacitor.

[0130] According to the foregoing invention, since the soft start meanschanges the oscillation frequency of the oscillation means at thestart-up, based on the charge amount of the capacitor which is increasedor decreased with time by the charge amount changing means, it becomespossible to easily prevent a rush current from flowing into thevoltage-increasing capacitor at the start-up. Besides, since thecapacitor of a desired type may be externally attached, it becomespossible to freely set how to change the oscillation frequency of theoscillation means at the start-up.

[0131] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0132] the soft start means includes counting means for counting thenumber of oscillations of the oscillation means; and

[0133] the soft start means detects a passage of time by counting thenumber of the oscillations by the counting means at the start-up, andchanges the oscillation frequency based on a detection result of thepassage of time.

[0134] According to the foregoing invention, since the soft start meansdetects the passage of time by counting the number of the oscillationsby the counting means at the start-up, and changes the oscillationfrequency of the oscillation means based on the detected passage oftime, it becomes possible to easily prevent a rush current from flowinginto the voltage-increasing capacitor at the start-up.

[0135] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0136] the switching means includes not less than one first switch forconnecting a path for charging the voltage-increasing capacitor in thecharge period and for cutting off the path for charging thevoltage-increasing capacitor in the voltage-increasing period, and notless than one second switch for cutting off a path for charging theoutput capacitor in the charge period and for connecting the path forcharging the output capacitor in the voltage-increasing period;

[0137] at least one of the first switch and the second switch is afield-effect transistor; and

[0138] the soft start means controls the switching means to carry outthe switching operation so as to exercise channel resistance control fordecreasing channel resistance with time when at least one field-effecttransistor is conducting, so as to prevent a rush current from flowinginto the output capacitor at the start-up.

[0139] According to the foregoing invention, under the control of thesoft start means, the switching means carries out the switchingoperation at the start-up so as to exercise the channel resistancecontrol for decreasing the channel resistance with time when at leastone field-effect transistor of the first switch and the second switch isconducting, so as to prevent a rush current from flowing into the outputcapacitor. Therefore, the output capacitor is gradually charged at thestart-up. Consequently, it becomes possible to easily prevent anovershoot of the output voltage at the start-up. Besides, since no rushcurrent flows, the current rating of the field-effect transistor can beset lower.

[0140] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0141] the soft start means includes a capacitor and charge amountchanging means for increasing or decreasing a charge amount of thecapacitor with time at the start-up; and

[0142] the soft start means controls the switching means to carry outthe switching operation so as to exercise the channel resistance controlat the start-up, based on the charge amount of the capacitor.

[0143] According to the foregoing invention, the soft start meanscontrols the switching means to decrease the channel resistance when thefield-effect transistor is conducting at the start-up, based on thecharge amount of the capacitor increased or decreased with time by thecharge amount changing means. Therefore, it becomes possible to easilyprevent a rush current from flowing into the output capacitor at thestart-up. Besides, since the capacitor of a desired type may beexternally attached, it becomes possible to freely set how to decreasethe channel resistance of the field-effect transistor at the start-up.

[0144] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0145] the stabilized power unit includes switching signal generationmeans for generating a switching signal constituted by a pulsecorresponding to the switching operation;

[0146] the soft start means includes counting means for counting thenumber of pulses of the switching signal generated by the switchingsignal generation means; and

[0147] the soft start means detects a passage of time by counting thenumber of the pulses by the counting means at the start-up, and controlsthe switching means to carry out the switching operation so as toexercise the channel resistance control, based on a detection result ofthe passage of time.

[0148] According to the foregoing invention, since the soft start meansdetects the passage of time by counting the number of the pulses of theswitching signal generated by the switching signal generation means bythe counting means at the start-up, and controls the switching means todecrease the channel resistance when the field-effect transistor isconducting, based on the detected passage of time, it becomes possibleto easily prevent a rush current from flowing into the output capacitorat the start-up.

[0149] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0150] the switching means includes (a) output voltage detection meansfor detecting the output voltage, (b) reference voltage generation meansfor generating a reference voltage so as to be voltage-adjustable, and(c) comparison means which compares a detected value of the outputvoltage detected by the output voltage detection means with thereference voltage, and controls the switching means to stop theswitching operation in a condition that a charge from thevoltage-increasing capacitor to the output capacitor is not carried outwhen the detected value becomes not less than the reference voltageduring the switching operation, or controls the switching means to carryout the switching operation when the detected value decreases by apredetermined value while the switching operation is stopped; and

[0151] the soft start means controls the reference voltage generationmeans to increase the reference voltage to a predetermined value so asto prevent a rush current from flowing into the voltage-increasingcapacitor at the start-up.

[0152] According to the foregoing invention, the switching means may bestructured so as to compare the detected value of the output voltagedetected by the output voltage detection means with the referencevoltage generated by the reference voltage generation means so as to bevoltage-adjustable, by the comparison means. When the detected value isnot less than the reference voltage during the switching operation, thecomparison means controls the switching means to stop the switchingoperation so as not to carry out the charge from the voltage-increasingcapacitor to the output capacitor, and when the detected value isdeclined by the predetermined value while the switching operation isstopped. On the other hand, the soft start means controls the referencevoltage generation means to increase the reference voltage to apredetermined value so as to prevent a rush current from flowing intothe voltage-increasing capacitor at the start-up. With this structure,the output capacitor is gradually charged in the voltage-increasingperiod. Consequently, it becomes possible to easily prevent an overshootof the output voltage at the start-up.

[0153] Besides, since the structure by which the soft start meanscontrols the reference voltage generation means to increase thereference voltage can be designed very easily, complicated processes arenot required and a chip area can be reduced when the structure is madeup in a chip, and thus a soft start function can be attachedinexpensively.

[0154] Further, to achieve the foregoing object, the stabilized powerunit of the present invention may be structured such that:

[0155] the soft start means includes a capacitor and charge amountchanging means for increasing or decreasing a charge amount of thecapacitor with time at the start-up; and

[0156] the soft start means controls the reference voltage generationmeans to increase the reference voltage to the predetermined value atthe start-up, based on the charge amount of the capacitor.

[0157] According to the foregoing invention, since the soft start meansincreases the reference voltage of the reference voltage generationmeans at the start up based on the charge amount of the capacitorincreased or decreased with time by the charge amount changing means, itbecomes possible to easily prevent a rush current from flowing into theoutput capacitor at the start-up. Besides, since the capacitor of adesired type may be externally attached, it becomes possible to freelyset how to increase the reference voltage of the reference voltagegeneration means at the start-up.

[0158] The stabilized power unit of the present invention can be astabilized power unit which includes:

[0159] an voltage-increasing capacitor which is charged based on aninput voltage and whose voltage is increased after being charged;

[0160] switching means for carrying out switching operation toalternately switch a charge period and a voltage-increasing period ofthe voltage-increasing capacitor;

[0161] an output capacitor which outputs a charged voltage utilizing avoltage-increasing potential of the voltage-increasing capacitor in thevoltage-increasing period, as an output voltage; and

[0162] soft start means for controlling the switching means to carry outthe switching operation which increases and decreases the output voltagewithin the range of the output voltage so that the charged voltage ofthe output capacitor is stabilized within the range of the outputvoltage in the steady state.

[0163] According to the foregoing invention, at the start-up, the softstart means controls the switching means to carry out the switchingoperation which increases and desreases the output voltage within therange of the output voltage so that the charged voltage of the outputcapacitor is stabilized within the range of the output voltage in thesteady state. With this structure, the charged voltage of the outputcapacitor becomes stabilized within the range of the output voltage inthe steady state, without having an overshoot until the completion ofthe start-up. Consequently, it becomes possible to provide aswitched-capacitor-type stabilized power unit which can prevent anovershoot of the output voltage at the start-up, in the structure havingthe output capacitor which outputs the charged voltage obtained througha plurality of charges by the switching operation utilizing avoltage-increasing potential of the voltage-increasing capacitor, as anoutput voltage.

[0164] As the method for starting up the stabilized power unit of thepresent invention which includes:

[0165] switching means for carrying out switching operation toalternately switch a charge period and a voltage-increasing period ofthe voltage-increasing capacitor; and

[0166] an output capacitor which outputs a charged voltage obtained bybeing charged utilizing a voltage-increasing potential of thevoltage-increasing capacitor in the voltage-increasing period, as anoutput voltage,

[0167] wherein:

[0168] the charged voltage is stabilized within a range of the outputvoltage in steady state through a plurality of the voltage-increasingperiods after a start-up is started,

[0169] the method includes the step of:

[0170] carrying out the switching operation so that the charged voltagealways becomes not more than the output voltage in the steady state, atthe start-up from when the start-up is started until when the chargedvoltage is stabilized within the range of the output voltage in thesteady state.

[0171] According to the foregoing invention, at the start-up, theswitching operation is carried out so that the charged voltage of theoutput capacitor always becomes not more than the output voltage in thesteady state. With this structure, the charged voltage of the outputcapacitor becomes stabilized within the range of the output voltage inthe steady state, without having an overshoot until the completion ofthe start-up. Consequently, it becomes possible to provide aswitched-capacitor-type stabilized power unit which can prevent anovershoot of the output voltage at the start-up, in the structure havingthe output capacitor which outputs the charged voltage obtained througha plurality of charges by the switching operation utilizing avoltage-increasing potential of the voltage-increasing capacitor, as anoutput voltage.

[0172] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A stabilized power unit, comprising: anvoltage-increasing capacitor which is charged based on an input voltageand whose voltage is increased after being charged; switching means forcarrying out switching operation to alternately switch a charge periodand a voltage-increasing period of the voltage-increasing capacitor; anoutput capacitor which outputs a charged voltage obtained by beingcharged utilizing a voltage-increasing potential of thevoltage-increasing capacitor in the voltage-increasing period, as anoutput voltage, and stabilizes the charged voltage within a range of theoutput voltage in steady state through a plurality of thevoltage-increasing periods after a start-up is started; and soft startmeans for controlling the switching means to carry out the switchingoperation so that the charged voltage always becomes not more than theoutput voltage in the steady state, at the start-up from when thestart-up is started until when the charged voltage is stabilized withinthe range of the output voltage in the steady state.
 2. A stabilizedpower unit, comprising: an voltage-increasing capacitor which is chargedbased on an input voltage and whose voltage is increased after beingcharged; switching means for carrying out switching operation toalternately switch a charge period and a voltage-increasing period ofthe voltage-increasing capacitor; an output capacitor which outputs acharged voltage utilizing a voltage-increasing potential of thevoltage-increasing capacitor in the voltage-increasing period, as anoutput voltage; and soft start means for controlling the switching meansto carry out the switching operation which increases and desreases theoutput voltage within the range of the output voltage in the study stateso that the charged voltage of the output capacitor is stabilized withinthe range of the output voltage in the steady state.
 3. The stabilizedpower unit as set forth in claim 1, wherein: the soft start meanscontrols the switching means so as to carry out the switching operationso that the charge period is gradually prolonged to a predeterminedvalue, so as to prevent a rush current from flowing into thevoltage-increasing capacitor at the start-up.
 4. The stabilized powerunit as set forth in claim 3, wherein: the soft start means includes acapacitor and charge amount changing means for increasing or decreasinga charge amount of the capacitor with time at the start-up; and the softstart means determines the charge period at the start-up based on thecharge amount of the capacitor.
 5. The stabilized power unit as setforth in claim 4, wherein: the charge amount changing means includes aconstant current source and a Zener diode, and Zener voltage of theZener diode is set higher than a reference voltage of the soft startmeans.
 6. The stabilized power unit as set forth in claim 3, wherein:the soft start means includes oscillation means for carrying outoscillation at a predetermined oscillation frequency and counting meansfor counting the number of oscillations of the oscillation means; andthe soft start means detects a passage of time by counting the number ofthe oscillations by the counting means at the start-up, and determinesthe charge period based on a detection result of the passage of time. 7.The stabilized power unit as set forth in claim 6, wherein: theoscillation means carries out oscillation of a triangular wave voltageat a predetermined oscillation frequency, and the counting means (a)starts counting the number of oscillations of the triangular wavegenerated by the oscillation means at the start-up, and (b) outputs asignal for giving instruction which switch of plural switches in aswitch circuit should be in a connected state when the number of theoscillations counted by the counting means reaches a predeterminedvalue.
 8. The stabilized power unit as set forth in claim 7, wherein:the switch circuit makes a predetermined switch be in a connected stateso as to obtain the lowest voltage; and the counting means switches theswitches in the switch circuit for each threshold for the number of theoscillations generated by the oscillation means so as to increase thevoltage step by step.
 9. The stabilized power unit as set forth in claim3, wherein: the soft start means includes oscillation means for carryingout oscillation with an oscillation frequency changed from high to lowwith time at the start-up; and the soft start means determines thecharge period at the start-up, based on the oscillation frequency. 10.The stabilized power unit as set forth in claim 9, wherein: the softstart means includes a capacitor and charge amount changing means forincreasing or decreasing a charge amount of the capacitor with time atthe start-up; and the soft start means changes the oscillation frequencyat the start-up, based on the charge amount of the capacitor.
 11. Thestabilized power unit as set forth in claim 10, wherein: the chargeamount changing means includes a constant current source and a Zenerdiode, and Zener voltage of the Zener diode is set higher than areference voltage of the soft start means.
 12. The stabilized power unitas set forth in claim 9, wherein: the soft start means includes countingmeans for counting the number of oscillations of the oscillation means;and the soft start means detects a passage of time by counting thenumber of the oscillations by the counting means at the start-up, andchanges the oscillation frequency based on a detection result of thepassage of time.
 13. The stabilized power unit as set forth in claim 12,wherein: the oscillation means includes of an oscillator, and a clockcounter circuit, and the clock counter circuit counts the number ofoscillations of a triangular wave outputted from the oscillator, and isthe clock counter circuit which outputs a signal for changing theoscillation frequency of the oscillator from a high frequency to a lowfrequency to the oscillator, whenever the count reaches a predeterminedthreshold.
 14. The stabilized power unit as set forth in claim 1,wherein: the switching means includes not less than one first switch forconnecting a path for charging the voltage-increasing capacitor in thecharge period and for cutting off the path for charging thevoltage-increasing capacitor in the voltage-increasing period, and notless than one second switch for cutting off a path for charging theoutput capacitor in the charge period and for connecting the path forcharging the output capacitor in the voltage-increasing period; at leastone of the first switch and the second switch is a field-effecttransistor; and the soft start means controls the switching means tocarry out the switching operation so as to exercise channel resistancecontrol for decreasing channel resistance with time when at least onefield-effect transistor is conducting, so as to prevent a rush currentfrom flowing into the output capacitor at the start-up.
 15. Thestabilized power unit as set forth in claim 14, wherein: at least one ofthe second switches is constituted by a field-effect transistor.
 16. Thestabilized power unit as set forth in claim 14, wherein: the soft startmeans includes a capacitor and charge amount changing means forincreasing or decreasing a charge amount of the capacitor with time atthe start-up; and the soft start means controls the switching means tocarry out the switching operation so as to exercise the channelresistance control at the start-up, based on the charge amount of thecapacitor.
 17. The stabilized power unit as set forth in claim 16,wherein: the charge amount changing means includes resistors and aconstant voltage circuit.
 18. The stabilized power unit as set forth inclaim 14, wherein: the stabilized power unit includes switching signalgeneration means for generating a switching signal constituted by apulse corresponding to the switching operation; the soft start meansincludes counting means for counting the number of pulses of theswitching signal generated by the switching signal generation means; andthe soft start means detects a passage of time by counting the number ofthe pulses by the counting means at the start-up, and controls theswitching means to carry out the switching operation so as to exercisethe channel resistance control, based on a detection result of thepassage of time.
 19. The stabilized power unit as set forth in claim 1,wherein: the switching means includes (a) output voltage detection meansfor detecting the output voltage, (b) reference voltage generation meansfor generating a reference voltage so as to be voltage-adjustable, and(c) comparison means which compares a detected value of the outputvoltage detected by the output voltage detection means with thereference voltage, and controls the switching means to stop theswitching operation in a condition that a charge from thevoltage-increasing capacitor to the output capacitor is not carried outwhen the detected value becomes not less than the reference voltageduring the switching operation, or controls the switching means to carryout the switching operation when the detected value decreases by apredetermined value while the switching operation is stopped; and thesoft start means controls the reference voltage generation means toincrease the reference voltage to a predetermined value so as to preventa rush current from flowing into the voltage-increasing capacitor at thestart-up.
 20. The stabilized power unit as set forth in claim 19,wherein: the stabilized power unit has a chip structure.
 21. Thestabilized power unit as set forth in claim 19, wherein: the soft startmeans includes a capacitor and charge amount changing means forincreasing or decreasing a charge amount of the capacitor with time atthe start-up; and the soft start means controls the reference voltagegeneration means to increase the reference voltage to the predeterminedvalue at the start-up, based on the charge amount of the capacitor. 22.The stabilized power unit as set forth in claim 21, wherein: the chargeamount changing means is made up of resistors and a constant voltagecircuit.
 23. A method for starting up a stabilized power unit whichincludes: an voltage-increasing capacitor which is charged based on aninput voltage and whose voltage is increased after being charged;switching means for carrying out switching operation to alternatelyswitch a charge period and a voltage-increasing period of thevoltage-increasing capacitor; and an output capacitor which outputs acharged voltage obtained by being charged utilizing a voltage-increasingpotential of the voltage-increasing capacitor in the voltage-increasingperiod, as an output voltage, wherein: the charged voltage is stabilizedwithin a range of the output voltage in steady state through a pluralityof the voltage-increasing periods after a start-up is started, saidmethod comprising the step of: carrying out the switching operation sothat the charged voltage always becomes not more than the output voltagein the steady state, at the start-up from when the start-up is starteduntil when the charged voltage is stabilized within the range of theoutput voltage in the steady state.